Generally, an internal combustion engine does not produce torque when the timing of combustion starting (spark ignition timing or compression ignition timing) of a mixture in a cylinder thereof is lagged and conversely, an excessive advance in spark or firing timing causes knocking. Therefore, the timing of the combustion starting in a cylinder for an internal combustion engine is preferably set to proper timing (M B T: Minimum advance for Best Torque) for large torque within the extent that knocking does not occur, based upon an engine rotation speed, a throttle valve opening or the like. Patent Document 1, as a control apparatus for an internal combustion engine in order to provide such M B T, has disclosed a control apparatus which advances or retards the timing of combustion starting based upon a combustion rate in a cylinder. In the control apparatus, the combustion rate is determined based upon a heat generation rate or in-cylinder pressures at three points or more including crank angle timing for the combustion rate.
In addition, the above-mentioned M B T is in the vicinity of the spark ignition or compression ignition timing at which knocking possibly occurs and therefore, the timing of the combustion starting is advanced as much as possible while preventing occurrence of the knocking, thus making the timing of the combustion starting be close to the M B T and enabling generation of large torque in an internal combustion engine. Patent Document 2, as a control apparatus for an internal combustion engine to perform such M B T control, has disclosed a control apparatus which utilizes the phenomenon that a heat generation rate in a cylinder increases temporarily and also sharply caused by the occurrence of knocking. This control apparatus determines a heat generation rate from an in-cylinder pressure sampled by in-cylinder pressure detecting means and judges whether or not the engine is in nearly close to a state of the knocking based upon a changing rate of a heat generation rate in the region from a point the determined heat generation rate becomes the maximum to a point of combustion completion.
The above-mentioned conventional control apparatus for the internal combustion engine basically performs processing of the in-cylinder pressures detected by the in-cylinder pressure detecting means for every minute crank angle, thus providing the heat generation rate. As a result, the calculating loads in the conventional control apparatus become remarkably large and therefore, it is practically difficult to apply the conventional control apparatus to an internal combustion engine for a vehicle, for example. In addition, even if the combustion rate is determined based upon in-cylinder pressures at about three points by the conventional method, an accurate M B T control which is practically usable can not be achieved.
(Patent Document 1) Japanese Patent Application Laid-Open No. 9 (1997)-189281
(Patent Document 2) Japanese Patent Application Laid-Open No. 2 (1990)-204662